<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>作业</title>
    <style>
        div div {
            width: 50px;
            height: 50px;
            background-color: blue;
            border: 25px solid red;
            /*溢出隐藏*/
            /*overflow: hidden;*/
        }

        #t1 {
            display: block;
            /*默认情况下盒子模型计算方式: content-box*/
            /*如果改成border-box元素的宽度将包含:内容+内边距+边框 不包括外边距*/
            box-sizing: border-box;
            width: 100px;
            height: 100px;
            border: 5px solid green;
            margin-left: 100px;
            padding-left: 50px;
            padding-top: 50px;
            border-radius: 5px;
        }
    </style>
</head>
<body>
<div>
    <div></div>
</div>
<div id="t1">哈喽</div>

</body>
</html>